The invention relates to a method and apparatus for manufacturing wooden pallets, and more particularly to a method and apparatus wherein a single nailing machine is used for nailing both the top deckboards and the bottom deckboards to the stringers.
A method and apparatus of the type generally described above are disclosed in U.S. Pat. No. 4,392,600, which is incorporated herein by reference. According to the method and apparatus disclosed therein, each pallet is manufactured by first nailing the deckboards to one side of the pallet, preferably the bottom, then inverting the partially-completed pallet and nailing the deckboards to the opposite side. Horizontal transportation of the pallet during manufacture is provided by a horizontally-driven gripper carriage which engages the stringers. The gripper carriage pulls the stringers to the nailing station and stops at a predetermined point for the first deckboard to be nailed thereon, then advances a predetermined distance and again stops for the second deckboard to be nailed thereon, and proceeds in this manner until the first set of deckboards have been nailed to the stringers.
The gripper carriage includes a gripper assembly which has a forward set of grippers and a rearward set of grippers so that the gripper assembly can simultaneously grip two separate sets of stringers, one forwardly of the gripper assembly and one rearwardly thereof. The gripper assembly is rotatable about a transverse horizontal axis so that the pallet may be inverted while held by the gripper assembly by a turnover mechanism. After nailing of the first set of deckboards to the stringers, the nailing head pulls the partially completed pallet beyond the nailing head, then reverses direction to push the pallet into engagement with the turnover mechanism to invert it. After inversion, an empty set of grippers faces rearwardly. The gripper carriage then pulls the inverted, partially-completed pallet back through the nailing station, engages the forward ends of a second set of stringers, and then proceeds forward to push the partially completed pallet through the nailing station for attachment of the top deckboards thereto, pulling the second set of stringers along behind. After nailing of the top deckboards to the first set of stringers, the second set of stringers is pulled through the nailing station for the bottom set of deckboards to be nailed thereon. Once this has been completed, the gripper carriage advances forwardly to a predetermined point at which the first pallet, having been completed, is released. The gripper carriage then reverses direction to invert the second pallet and pick up a third set of stringers, repeating the steps described above.
The nailing operation in U.S. Pat. No. 4,392,600 involves vertical movement of a large, heavy nailing head which includes a plurality of punches for driving nails downwardly through the deckboard stringers. The nailing head is driven through a fixed stroke by a continuously rotating electric motor that is connected to the head by a crank arrangement, with a brake-clutch assembly interposed between the motor and the head so that the reciprocating movement of the head need not be continuous.
The present invention relates to a method and apparatus which provide many of the advantages of the method and apparatus set forth in U.S. Pat. No. 4,392,600, and additionally provide improved performance and durability for the apparatus.